East Mountain is a traprock mountain ridge located in the Connecticut River Valley of Massachusetts. It is part of the narrow, linear Metacomet Ridge that extends from Long Island Sound near New Haven, Connecticut, north through the Connecticut River Valley of Massachusetts to the Vermont border. East Mountain is known for its extensive scenic cliffs, unique microclimate ecosystems, and rare plant communities. It is traversed by the 110-mile (180 km) Metacomet-Monadnock Trail.